The present invention relates to dental apparatus and method and more particularly the invention is concerned with dental root canal apex measuring apparatus and method.
In root canal therapy, a dental probe, such a as a reamer or a file, is inserted into the canal and manipulated to remove undesired material. A flexible filler substance is then placed in the root canal that is sealed with rigid material. If the canal is not completely cleaned prior to filling and sealing, debris left inside the canal can prevent proper healing. The probe must therefore be inserted all the way to the apex of the root canal during cleaning to remove all debris. If, however, the probe is inserted too deeply, the tool penetrates the jaw tissue, causing swelling and unnecessary trauma for the patient. It is therefore essential to precisely determine when the probe tip has reached the root canal apex, so that the canal can be cleaned fully, without excessive trauma to the patient.
Locating the apex is difficult, because the narrow canal does not provide a clear viewing path and fluids can partially fill the canal. In one method, the probe is inserted into the canal and the tooth is X-rayed. In the X-ray image, the metal probe contrasts with the surrounding tooth and body tissue, so that the positions of the probe tip and the apex can be compared. If the probe tip is not at the apex, it is inserted deeper into the canal and a new X-ray image is obtained. This method is unreliable, time-consuming, costly, and exposes the patent to unnecessary X-ray radiation.
It is also known to locate the root apex by inserting a conductive probe into the root canal and placing an electrode in contact with the patient's body, usually in or near the mouth. As the probe is moved through the canal towards the apex, electrical measurements across the probe and electrode are made.
Examples of this latter method are described in several U.S. Patents.
U.S. Pat. No. 5,080,586 discloses locating the apex by making impedance measurements by driving two fixed frequencies and fixed amplitude sinus shape current as the probe is moved towards the apex. A detector determines that the probe tip is at the apex when the difference of the two impedance measurements is within a predetermined range. The device measures peak volt.
U.S. Pat. No. 5,096,419 discloses the apex by making impedance measurements by driving two fixed frequencies and fixed amplitudes sinus shape current as the probe is moved towards the apex. A detector determines that the probe tip is at the apex when the ratio of the two impedance measurements is within a predetermined range. The device measures a peak volt.
U.S. Pat. No. 6,425,875 discloses locating the apex by making impedance measurements by driving two fixed frequencies and fixed amplitude sinus shape current as the probe is moved towards the apex. A detector determines that the probe tip is at the apex by a defined Region A and a defined Region B. At Region A, the difference of the two impedances defines the location of the probe tip. In contrast, at Region B the ratio of the two impedances defines the location. The device measures RMS volts and can control the output impedance.